1. Field of the Invention
This invention relates to the catalytic reduction (hydrogenation) of halonitroaromatic compounds.
2. Description of the Prior Art
It is recognized in the art that the catalytic reduction of a halogen substituted aromatic nitro compound to the halogen substituted amine may be difficult to achieve because of the occurrence of extensive dehalogenation during the process. For example, Baltzley and Phillips disclose in the Journal of the American Chemical Society 68, 261 (1946) that removal of halogen atoms during catalytic hydrogenations of organic compounds is a familiar phenomenon and that most workers have considered such loss of halogen as inevitable. U.S. Pat. No. 2,791,613 discloses that hydrogenation processes are not generally suitable for converting halonitrobenzenes to haloanilines, primarily because considerable dehalogenation accompanies the reduction reaction. The patent further discloses that a meta-halonitrobenzene can be reduced to the corresponding aniline derivative with a minimum of dehalogenation by employing a copper-chromium oxide catalyst. U.S. Pat. No. 2,772,313 discloses a catalytic process employing rhodium for converting halonitrobenzenes to haloanilines with a minimum of dehalogenation. U.S. Pat. No. 3,073,865 discloses the hydrogenation of halogen substituted aromatic nitro compounds to the corresponding amines, the process being carried out in the presence of a platinum on carbon catalyst and controlled amounts of magnesium oxide or magnesium hydroxide to suppress dehalogenation. U.S. Pat. No. 3,145,231 discloses a process for reducing halogen substituted nirtoaromatic compounds with a minimum of dehalogenation, the process employing a platinum catalyst and a cycloaliphatic base, for example, morpholine. U.S. Pat. No. 3,474,144 discloses a catalytic hydrogenation process for producing chloroaniline. The process employs, for example, a nickel, platinum or palladium catalyst and triphenyl phosphite or tritolyl phosphite as a dechlorination inhibitor. Netherlands Patent Publication No. 73/11193 discloses the use of oxyacids of trivalent or pentavalent phosphorus and strong bases, or the corresponding salts, to maintain the pH at 6-7.5 during the nickel-catalyzed reduction of halogen substituted nitrobenzenes.